1. Field of the Invention
This invention relates to a key switch, and particularly to an improved key switch utilized, for example, as a safety switch of a door.
2. Description of the Related Art
A conventional safety switch of a door is mounted in a safety door or a care fence on equipment in order to prevent accidents by unprepared operations or accidental operations beforehand in various machine tools and industry equipment.
This kind of safety switch is designed to be inoperable with a tool, for example, a screw driver, except for an exclusive key, and lock its internal apparatus in an initial condition that the key is pulled out, an example of which is shown in FIGS. 32 and 33.
In this conventional safety switch, cam plate 104 is rotated by the insertion-and-pull-out movement of a key 103 as to a key insertion opening 102, and a plunger 105 coming into contact with a peripheral cam surface of the cam plate 104 is displaced in accordance with the rotational movement of the cam plate 104 so as to switch a switch mechanism (not shown in drawings), and there is provided a rotational lock mechanism for locking the rotation of the cam plate 104 in the initial position when the key 103 is pulled out.
This rotational lock mechanism 106 includes a pair of forward and backward locking members 107 disposed near the periphery of the cam for a forward-and-backward movement in a rotary axial direction "q" of the cam plate 104, and a spring 108 for urging the locking members 107 toward the cam 104, in which a lock pin 109 projecting from the locking member 107 is urged to be engaged with an engagement concave portion 110 formed at the periphery of the cam plate 104 so as to fix the cam plate 104 at the initial position.
Each locking member 107 includes a cam slant 111 directed to the key insertion opening 102 for lock release. As shown in FIG. 33, a point of the key 103 inserted in the key insertion opening 102 pushes the lock release cam slant 111 of each locking member 107 so as to move each locking member 107 backward against the spring 108 to release the locking for rotating the cam plate 104 by the subsequent insertion operation of the key 103
According to the conventional rotation lock mechanism 106 of the above-mentioned construction, the locking member 107 is disposed for a forward-and-backward movement in a rotary axial direction "q" of the cam plate 104, so that the arrangement space of the locking member 107 and the lock push spring 108 is large in the rotation axial direction "q" of the cam plate 104, so that the thickness of the whole switch in the forward and backward direction is bulky.
A pair of locking members 107 have to be disposed in front and back of the cam plate 104 to comply with the standard, whereby the space in the forward-and-backward direction of rotation lock mechanism 106 is enlarged causing a bulky key switch.